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Deep-Water Characteristics of the Trans-Pacific Tsunami from the 1 April 2014 Mw 8.2
Iquique, Chile Earthquake
MOHAMMAD HEIDARZADEH,1 KENJI SATAKE,1 SATOKO MUROTANI,1 ADITYA RIADI GUSMAN,1 and SHINGO WATADA1
Abstract—We studied the tsunami generated by the 1 April
2014 Mw 8.2 Iquique (Chile) earthquake using 20 Deep-ocean
Assessment and Reporting of Tsunamis (DART) records and
applying Fourier and wavelet analyses as well as performing
numerical simulations. Deep-water tsunami wave heights were in
the range of 0.8–35.0 cm. For the stations located more than
2,200 km from the source, the average wave height was
1.7 ± 1.1 cm. The observed tsunami arrivals were delayed by
1–17 min relative to the simulated ones based on the linear long
wave equations, and the delays were proportional to the tsunami
travel distances. A small initial depression was observed at DART
stations located at distances [10,000 km from the source whereas,
traditionally, an initial elevation is expected at stations located
seaward of subduction zones. Fourier analyses showed tsunami
governing periods of 21.1 ± 1.7 and 14.7 ± 0.7 min, corre-
sponding to a fault length of 60–70 km and a fault width of
40–45 km. While the two 21-min and 15-min signals appeared in
most DART stations during *0.5 h following the conventional
arrival times, the 15-min signal was delayed at some far-field
stations. Distribution of maximum DART wave heights across the
Pacific Ocean did not show a meaningful relation between maxi-
mum DART wave heights and directivity or distance from the
source.
Key words: Pacific Ocean, tsunami, Iquique earthquake of 1
April 2014, chilean tsunami, DART buoy, deep-water waves,
fourier analysis, wavelet analysis, numerical modeling.
1. Introduction
A trans-oceanic tsunami was observed across the
Pacific Ocean following the Mw 8.2 (USGS 2014) off
Iquique (Chile) earthquake of 1 April 2014. The epi-
center was at 19.610�S and 70.776�W (Fig. 1), with a
depth of around 25 km and the origin time at 23:46:47
UTC (USGS 2014). The earthquake caused a death
toll of at least seven in Chile and left over 200 injured
(IOC-ITIC 2014). No fatality was reported due to the
tsunami although some damage to coastal areas was
reported. According to the Pacific Tsunami Warning
Center (PTWC 2014), the tsunami waves reached
almost all coastal areas within the Pacific Ocean
registering maximum trough-to-crest tide gauge wave
heights of: 4.25 m in Iquique (Chile), 1.17 m in
Matarani (Peru), 0.32 m in Salina Cruz (Mexico),
1.09 m in Hiva Oa (French Polynesia), 0.33 m in
Crescent City (California, USA), 1.13 m in Hilo
(Hawaii, USA), 0.61 m in Waitangi (New Zealand),
0.71 m in American Samoa, 0.4 m in Vanuatu, and
0.34 m in Hakodate (Japan) (see Fig. 1 for locations).
The tsunami waves were also recorded on Deep-
ocean Assessment and Reporting of Tsunamis sta-
tions (DART) across the Pacific Ocean.
Development and deployment of DART buoys in
world’s oceans in recent years have provided an
opportunity to obtain refined information about
tsunami sources and to better understand deep-water
characteristics of tsunami propagation, in addition
to its primary function as a vital part of tsunami
warning systems. In this context, DART records of
tsunamis have been efficiently used in tsunami
research. RABINOVICH et al. (2013a) studied open
ocean energy decay of tsunamis by analyzing
DART records of some recent trans-Pacific tsuna-
mis. OKAL et al. (2014) applied DART records of
Pacific tsunamis along with other simulated ones to
develop a formula relating earthquake size to far-
field tsunami amplitude. HEIDARZADEH and SATAKE
(2013a) studied the source spectra of the 11 March
2011 Tohoku tsunami through its DART records.
WATADA et al. (2014) employed DART waveforms
of recent tsunamis to explain arrival time delays
1 Earthquake Research Institute (ERI), The University of
Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan. E-mail:
Pure Appl. Geophys.
� 2014 Springer Basel
DOI 10.1007/s00024-014-0983-8 Pure and Applied Geophysics
and initial phase reversal relative to simulated tsu-
namis in the far-field. Here we study open-ocean
characteristics of the 2014 off Iquique (Chile) tsu-
nami by analyzing 20 DART records (Fig. 1). Main
targets are: tsunami source periods, distribution of
tsunami energy over time and frequency domains,
and deep-water tsunami wave heights and their
distribution within the Pacific Basin.
Figure 1a Initial seafloor deformation due to the 1 April 2014 Iquique (Chile) earthquake based on our fault model (see Sect. 2.3). The asterisk shows
the epicenter. b Bathymetry of the Pacific Ocean. The small red rectangle shows the location of a. The yellow circles are the locations of the
DART stations used in this study. c Location of the epicenter (black star) and distribution of maximum trough-to-crest wave heights recorded
on each DART station (circles) for the 2014 Iquique (Chile) tsunami. The color map shows distribution of the maximum tsunami amplitudes
in each grid point during the entire Pacific-wide tsunami simulations. Black and white numbers are DART names and maximum trough-to-
crest wave heights (in cm) for each DART station, respectively. The solid black arrow represents the normal direction to the fault strike. Small
filled rectangles show some major cities. Characters A–E show locations with large wave amplitudes that are not located normal to the fault
strike
M. Heidarzadeh et al. Pure Appl. Geophys.
2. Data and Methodology
The data used in this study include 20 DART
records with sampling intervals of 1 min provided by
the US National Oceanic and Atmospheric Admin-
istration (NOAA 2014) (Table 1; Fig. 1). The water
depth at the DART locations is in the range of
1,826–5,895 m indicating that only deep-water
characteristics of the 2014 Iquique tsunami can be
studied with such a dataset. Our methodology is a
combination of statistical and spectral analyses of the
observed tsunami waveforms along with numerical
modeling. In the following, each method is briefly
explained.
2.1. Waveform Preparation
The original DART data are provided with
different sampling intervals of 15 s, 1 min, and
15 min. As discussed by RABINOVICH et al. (2013a),
during a tsunami event, the buoys are switched
from the 15-min mode to the 15-s mode for
several minutes and then transmit 1-min data until
the end of the event. Switching between different
Table 1
The DART stations used to study the April 2014 Iquique tsunami along with characteristics of the tsunami waveforms
DART
station
Location Depth
(m)
Dist.
(km)a
Az.
(�)a
TT
(hh:mm)b
h (cm)c h5,000
(cm)d
Governing periods
(min)
hsim (cm)f Initial
polarityg
Lon.
(�E)
Lat.
(�N)
21414 178.26 48.95 5,375 13,160 315.66 17:47 1.3 1.3 21.6, 15.1 1.4 NAh
21418 148.77 38.69 5,662 15,679 307.69 20:28 1.4 1.4 21.6, 13.7 1.5 NA
21419 155.74 44.46 5,318 14,932 313.50 19:43 1.0 1.0 18.9, 15.1 1.1 NA
32401 -73.43 -20.47 4,865 288 251.02 0:18 35.0 34.8 21.6, 16.2 32.8 (?)
32402 -73.98 -26.74 4,070 853 201.79 0:58 6.6 6.3 21.6, 13.7 6.2 (?)
32411 -90.84 05.01 3,277 3,510 319.15 5:17 0.8 0.7 21.6, 15.1 0.7 NA
32412 -86.34 -17.98 4,387 1,644 273.87 2:07 10.8 10.5 21.6, 15.1 11.0 (?)
32413 -93.50 -7.40 3,890 2,800 295.83 3:40 5.3 5.0 21.6, 15.1 6.0 (?)
43412 -107.00 16.07 3,235 5,606 312.42 8:08 1.6 1.4 21.6, 13.7 1.8 NA
46402 -164.02 51.07 4,760 11,916 318.80 16:36 1.5 1.5 18.9, 15.1 1.4 (-)
46407 -128.81 42.67 3,322 9,120 320.81 13:26 1.3 1.2 19.8, 14.1 1.4 (-)
46409 -148.52 55.30 4,200 11,048 325.53 16:10 1.2 1.1 21.6, 15.1 1.3 (-)
46411 -127.02 39.35 4,259 8,779 318.93 12:52 1.5 1.4 19.0, 14.8 1.7 (?)
46412 -120.57 32.46 3,770 7,847 316.75 11:36 1.4 1.3 21.6, 15.1 1.8 NA
51407 -156.59 19.59 4,737 10,311 289.74 13:57 2.1 2.1 21.6, 15.1 1.8 (-)
51426 -168.29 -23.30 5,659 9,880 245.75 13:39 2.4 2.5 18.9, 13.7 2.7 (-)
52401 155.77 19.26 5,578 15,151 277.64 20:26 1.5 1.5 25.2, 13.7 2.1 NA
52402 154.04 11.87 5,875 15,156 266.75 20:20 0.9 0.9 30.2, 18.9, 13.7 1.4 NA
52405 132.18 12.99 5,895 17,459 256.80 23:45 1.0 1.0 24.2, 18.1, 14.5 0.8 NA
52406 165.00 -05.29 1,826 13,317 251.65 18:37 3.2 2.5 18.9, 15.1, 10.8 2.8 NA
Average and standard
deviations
1.7 ± 1.1e 21.1 ± 1.7, 14.7 ± 0.7i 1.8 ± 1.2e
a Distance (Dist.) and Azimuth (Az.) of every DART station to the epicenter are based on an spherical earth systemb Tsunami travel time (hour:min)c h is the observed maximum trough-to-crest wave heightd Normalized wave heights at a water depth of 5,000 m using Green’s law: h5;000 ¼ h d
5;000
� �1=4
, where h is the observed wave height, and d is
the water depth at the location of DART stations in meterse Without considering near-field stations with distances \20� (*2,200 km)f Simulated maximum trough-to-crest wave heightg Either initial elevation (?) or depression (-)h Not applicablei For calculating the average values, the periods from DART-52402 were excluded
Iquique Tsunami of April 2014 in the Pacific Ocean
sampling modes is problematic causing some gaps
and spikes as well as producing some repeating
data points. Careful data processing of the original
data was performed by removing gaps, spikes, and
repeating values, and by making sure that the
sampling interval is 1 min for the entire record.
The data length varies from around 5 h to 12 h.
Two different methods were used for de-tiding: (1)
estimating tidal signals by polynomial fitting and
then removing them from the original records and
(2) high-pass filtering. For polynomial fittings, a
polynomial of degree 10 was used for which we
applied the function ‘‘polyfit’’ in the Matlab
program (MATHWORKS 2014). For high-pass
filtering, the ‘‘Butterworth IIR’’ digital filter from
the Matlab signal processing toolbox is employed
for which a cutoff frequency of 0.0002–0.0003 Hz
(about 1–1.5 h) was chosen (MATHWORKS
2014). The reason for using two different methods
was to make sure that our de-tiding process is
sound. Figure 2 shows examples of de-tiding of
the original records of three DARTs using the two
methods mentioned above, indicating that the
resulting de-tided waveforms from them are sim-
ilar. We did not apply harmonic analysis for tidal
predictions because such an analysis was not
fruitful due to the short lengths of the 1-min
DART data.
2.2. Fourier and Wavelet Analyses
Fourier analysis was performed using the fast
Fourier transform (FFT) method for which the
‘‘FFT’’ function in Matlab program was used
(MATHWORKS 2014; HEIDARZADEH and SATAKE
2014b). Only the first 2.5 h of the tsunami waveforms
were used for Fourier analysis in order to prevent
reflected waves from appearing in our spectral
analysis. Usually, tsunami waveforms at DART
stations are free from local/regional bathymetric
effects; however, in a Pacific-wide scale, still some
reflected waves and regional bathymetric effects may
be present in the recorded waveforms because many
islands, seamount chains, and submarine ridges exist
within the Pacific Ocean.
Since a tsunami is a non-stationary phenomenon,
i.e., its spectral content varies with time, application of
wavelet analysis is useful to better understand its
behavior. Phenomena such as wave scattering, reflec-
tion, refraction, and dispersion can be studied by
wavelet analysis, which treats tsunami waveforms both
in time and frequency domains (RABINOVICH and
THOMSON 2007; HEIDARZADEH and SATAKE 2013a, b,
2014a; BORRERO and GREER 2013). For wavelet analysis,
we applied the wavelet package by TORRENCE and
COMPO (1998) using the ‘‘Morlet’’ mother function with
a wavenumber of 6 and a wavelet scale width of 0.10.
Figure 2a Original records along with tide predictions using polynomial fittings. b De-tided waveforms by subtracting the predicted tidal signals from
the original records. c De-tided waveforms using high-pass filtering
M. Heidarzadeh et al. Pure Appl. Geophys.
2.3. Numerical Modeling
We performed basin-wide tsunami simulations
using a linear shallow water numerical model on a
spherical coordinate system (model COMCOT, LIU
et al. 1998). A 5-min bathymetric grid resampled
from the 1-min GEBCO bathymetry grid (IOC et al.
2003) was used (Fig. 1). The time step for numerical
modeling was 6.0 s, and simulations were conducted
for a total time of 28.0 h. For tsunami simulations, we
used a single rectangular fault with parameters of
length 120 km, width 80 km, uniform slip 3.35 m,
depth 10 km, strike 351�, dip 12�, and rake 91�.
These source parameters were a combination of those
reported by USGS (2014) and those obtained by our
own source analysis (GUSMAN et al. 2014). As our
purpose is to understand deep-water wave character-
istics, not the source heterogeneity, we assumed a
single fault with uniform slip. Before finalizing the
fault parameters, a sensitivity analysis was performed
by changing the slip amount in the range 3–5 m in
order to reach the best slip value to reproduce the
observed waveforms. Simulated tsunami waveforms
were recorded at the location of each DART station.
3. Tsunami Waveforms and Their Properties
The results of de-tiding of 20 DART records using
polynomial fits and high-pass filters were the same
(Fig. 2); except for DARTs 32413, 52401, and 52405.
We applied the former method for de-tiding in our
study except in the aforesaid stations where the results
of the latter method were adopted (Fig. 3). The tsu-
nami signal was observed in all of the DART records
indicating the trans-oceanic nature of the tsunami. The
observed tsunami arrivals were delayed by 1–17 min
relative to the simulated ones depending on the
locations of the stations (Fig. 3). The travel time dif-
ferences between observations and linear shallow-
water simulations, based on a visual pick of the first
positive peaks, are shown at the bottom-right corners
of the panels (Fig. 3). The arrival time delays of the
observed waves relative to the simulated ones in the
far-field were attributed to the elastic loading of tsu-
namis, compressibility of sea water, and geopotential
variations associated with the motion of mass during
tsunami propagation as these effects are not included
in the numerical simulations (WATADA et al. 2014).
Despite the arrival delays, the simulated and observed
waveforms agree well in terms of amplitudes and
periods. Such a good agreement using a single fault
with uniform slip is not unusual because far-field
tsunami propagation is not very much sensitive to the
details of the tsunami source (TITOV et al. 2005).
An unusual long-period initial wave was observed
at DART 52401, which was also reproduced by
simulations. A similar initial wave was seen in sim-
ulations at DART 52405, but it is hard to identify it in
the observed record due to the high noise level
(Fig. 3). These long initial waves are possibly the
results of reflection/refraction/scattering of the tsu-
nami within the western Pacific Ocean, which is
heavily dominated by a wide range of bathymetric
features and islands (e.g., Polynesian, Micronesian,
and Melanesian Islands).
To better understand factors affecting the arrival
time differences between the observed waveforms
and the simulated ones based on the shallow water
equations, we plotted these delays versus the dis-
tances of the DART stations from the source
(Fig. 4a), versus the angles from the fault strike
(Fig. 4b), versus the DART tsunami wave heights
(Fig. 4c), and versus the combined effect of the dis-
tances and the angles (Fig. 4d). A clear positive
correlation can be seen between the source distances
and the arrival time delays (Fig. 4a). The largest
arrival time delays appear to be concentrated around
the normal direction to the fault strike (Fig. 4b, d).
However, such a relationship is not strongly sup-
ported by our data. Just a few DART stations far from
the epicenter happened to be located in the normal
direction to the trench off the coast of Chile. In other
words, the most important factor for the generation of
these arrival delays is distance from the source.
Almost no relationship can be seen between the deep-
water wave heights and arrival time delays, at least
for the 2014 Iquique tsunami (Fig. 4c).
3.1. Polarity of the Initial Phase
As for the polarity of the initial phase, it was not
possible to identify the initial phase at some stations
because the noise level was relatively high (Fig. 3).
Iquique Tsunami of April 2014 in the Pacific Ocean
M. Heidarzadeh et al. Pure Appl. Geophys.
For stations with low noise level, we determined the
polarity of the initial phase (Table 1). Classically, we
expect an initial elevation in the seaward of subduc-
tion zones; however, the waveforms in Fig. 3 indicate
an initial depression at stations located farther than
10,000 km from the source (Table 1). Although the
first stages of the waveforms are not very clear, an
initial depression cannot be overlooked, at least, at a
few stations, e.g., DARTs 46407, 51407, and 46409.
Phase reversal of tsunamis in the far-field has been
reported by some authors (OKAL 2011; RABINOVICH
et al. 2013b). According to WATADA et al. (2014), this
observed initial phase reversal at far-field DARTs is a
characteristic response of the self-gravitating elastic
Earth to tsunami loading, which causes reverse
dispersion of long waves. According to this theory,
if the initial phase at the tsunami source is positive
seaward (e.g., for subduction thrust earthquakes), the
recorded initial phase at far-field DARTs becomes
negative. On the other hand, if the initial phase at the
source is negative seaward (e.g., for normal-fault
earthquakes), the recorded initial phase at far-field
DARTs becomes positive.
3.2. Distribution of Tsunami Energy in the Far-Field
Distribution of maximum tsunami amplitudes by
numerical modeling (Fig. 1c) shows that most of the
tsunami energy is directed towards south and west of
the Pacific Ocean, which can be attributed to the
effect of tsunami directivity in the far-field.
Figure 4The arrival time delays of the observed waveforms relative to the simulated ones versus the distances from the source (a), versus the angles
from the fault strike (angle U) (b), and versus the tsunami wave heights (c). d The combined effect of the distance and the angle from the fault
strike on the arrival time delays
Figure 3Tsunami waveforms (thick-blue lines) generated by the 1 April
2014 (Chile) earthquake along with respective spectra. Thin-purple
lines represent simulated tsunami waveforms. The red dashed-
vertical line represents the origin time of the earthquake. The
numbers in boxes at the bottom of the panels are the time shifts
applied to the simulated waveforms in order to match the
observations. The values on vertical axes for the frequency plots
are omitted because the absolute amounts of spectral energy are not
important in this study. However, the amounts of spectral energy
are given in Fig. 6
b
Iquique Tsunami of April 2014 in the Pacific Ocean
According to the directivity of tsunami in the far-field
of a thrust or normal fault (BEN-MENAHEM and
RESENMAN 1972), the largest tsunami waves are
expected at the normal direction to the fault strike.
As the source fault is trending NNW–SSE (Fig. 1a),
most of the tsunami energy is expected to travel in the
SW direction according to the directivity effect (along
the solid-black arrow in Fig. 1c). However, the effects
of bathymetric features on tsunami energy distribution
are also evident in Fig. 1c. Some of high-energy
channels coincide with the locations of submarine
seamount chains and ridges in the Pacific Basin
(locations A–E in Fig. 1c). In fact, these bathymetric
features act as waveguides (SATAKE 1988; TITOV et al.
2005) or as scattering provinces (MOFJELD et al. 2001).
The effect of seafloor bathymetry on far-field prop-
agation of tsunamis was discussed by (SATAKE 1988).
Four factors, i.e., directivity, refraction, reflection, and
scattering, seem to affect far-field propagation of
tsunamis in the Pacific Basin.
3.3. Distribution of Maximum Deep-Water Wave
Heights
Among the analyzed stations, the maximum
trough-to-crest tsunami height was recorded at the
nearest station, i.e., DART 32401, with a value of
35.0 cm (Table 1; Fig. 1c). Except for the near-field
DART stations (those located at the distances
of \20�), the deep-water tsunami heights are in the
range of 0.8–5.3 cm with an average value of
1.7 ± 1.1 cm (Table 1). Distribution of maximum
wave heights in Fig. 1c may indicate that deep-water
wave heights are not much sensitive to the distance of
a DART station from the source or even to the
directivity effect. To better examine this hypothesis,
we plotted maximum deep-water wave heights versus
azimuth (Fig. 5a), versus the angles of the DART
stations from the fault strike (Fig. 5b), versus the
distances from the source (Fig. 5c), and versus both
effects together (Fig. 5d). To remove the effects of
different water depths at the locations of DARTs on
Figure 5a Tsunami wave height at each DART station as a function of azimuth of each station. b Tsunami wave heights versus the angles from the
fault strike. c Tsunami wave heights versus the distances of the DART stations from the source. The horizontal dashed line represents the
average value of DART trough-to-crest wave heights. d Distribution of the maximum tsunami heights versus distances from the tsunami
source and angles from the fault strike
M. Heidarzadeh et al. Pure Appl. Geophys.
the recorded wave heights, we normalized the
recorded heights to the water depth of 5,000 m using
Green’s law (Table 1). In an ideal case, we expect to
see tsunami wave heights decreasing toward both
sides of the right angle from the fault strike (U = 90�in Fig. 5b), and also decreasing by increasing the
distance from the source up to 10,000 km (90�),and
increasing again with the distance. Figure 5b–d does
not show such trends. This is possibly because of the
combined effect of the four factors of directivity,
refraction, reflection, and scattering on far-field
tsunami propagation. For example, although DART
52405 is located normal to the fault strike, it received
a wave height of 1.0 cm which is among the
minimum values recorded during this tsunami. This
is because DART 52405 is located within the
Philippines Sea where tsunami waves cannot pene-
trate easily due to the presence of numerous islands
and seamount chains at its border.
4. Results of Fourier Analysis
The respective spectrum for each observed
waveform is shown in Fig. 3. The spectra are rela-
tively simple with two major peaks around 21 min
and 15 min in most of the stations (Table 1). To
better compare the spectra from different DART
stations, they are overlaid in Fig. 6 for the near-field
(Fig. 6a), the middle range (Fig. 6b), and the far-field
stations (Fig. 6c). Because the level of spectral
energy is different from station to station, we equal-
ized the amounts of spectral energy by amplifying
factors. It can be seen that the spectra from across the
Pacific Ocean are similar to each other emphasizing
the fact that they contain mostly tsunami source
characteristics, and are almost free of non-tsunami
sources (RABINOVICH et al. 2013a). However, for sta-
tions far from the tsunami source, the spectra are
slightly diverging from each other (Fig. 6c) although
still the two major peaks at periods of *21 min
and *15 min are clear.
Figure 6d presents averaged spectra for the near-
field, the far-field, and all DART stations. The near-
field average spectrum (Fig. 6d, red line) is similar to
that of the far-field (Fig. 6d, blue line) implying that
the DART records of this tsunami, even in the far-field,
are free of non-tsunami sources. According to Table 1
and Fig. 6, the governing tsunami periods are:
21.1 ± 1.7 min and 14.7 ± 0.7 min. By assuming an
average and constant water depth of around 1,000 m at
the tsunami source, these governing periods imply a
Figure 6Comparison of the spectra of tsunami waveforms resulting from the 1 April 2014 Iquique earthquake recorded at DART stations in the near-
field (a), in the middle range (b), and in the far-field (c). Numbers in parentheses are amplifying factors used to multiply the original spectra in
order to facilitate their comparison. d Average spectra of the tsunami for the near-field (red-thin line; average of spectra in a), the far-field
(blue-thin line; average of spectra in c), and all DART stations (black-solid line)
Iquique Tsunami of April 2014 in the Pacific Ocean
M. Heidarzadeh et al. Pure Appl. Geophys.
source dimension of (60–70) km [length in strike
direction] 9 (40–45) km [width in dip direction] for
the tsunami source using the method described by
RABINOVICH and THOMSON (2007). This estimate is close
to the largest parts of the slip distribution by An et al.
(2014), and GUSMAN et al. (2014) obtained by tsunami
waveform inversion.
5. Results of Wavelet Analysis
Figure 7 presents the results of wavelet analysis.
The white lines represent the tsunami arrival times of
the first elevation phase which we designate here as
the conventional arrival time. Wavelet plots show
that at most stations, the longer wave components
with periods [22 min arrive earlier than the shorter
components. This is possibly due to the dispersion
effect; waves with longer periods travel faster than
the shorter ones. Such a normal dispersion is a
characteristic feature of gravity waves in the ocean
(deviation from long waves) and is not related to the
elasticity of the earth, compressibility of seawater, or
geopotential variations because these three effects
generate reverse dispersion at very long periods
(WATADA et al. 2014).
In general, the wavelet plots (Fig. 7) show that the
tsunami energy is concentrated in the period band of
around 12–25 min and is relatively less scattered in
comparison to that for tide gauge records of tsunamis
(e.g., RABINOVICH and THOMSON 2007; HEIDARZADEH
and SATAKE 2014a). In other words, the period band
of tsunami energy shown in Fig. 7 is relatively free
from non-tsunami sources. As for the arrival times
and temporal behavior of the two governing periods
of around 21 min and 15 min, Fig. 7 shows that the
two periods corresponding to the tsunami source
appear at many stations during *0.5 h following the
conventional arrival times. However, at DARTs
52402, 21418, and 52405, the first stages of tsunami
oscillations are dominated by the 21-min signal, and
then the 15-min signal appears.
Switching of the tsunami governing period from
one period to another at different times is observed.
For example, at DART 32402, the period of around
21 min is governing at early stages of tsunami arri-
val; then the period of around 15 min is governing
between 2:00 and 3:00 a.m.; later the two peak
periods of *21 min and *15 min are of similar
strength. Similar behavior can be seen more or less in
other stations. This behavior is indicative of the non-
stationary nature of tsunami waves.
6. Conclusions
The tsunami from the 1 April 2014 Iquique
(Chile) was studied using waveforms recorded at 20
DART stations. The main findings are:
1. Deep-water tsunami wave heights were in the
range 0.8–35.0 cm. For the stations located in the
far-field, the average wave height was
1.7 ± 1.1 cm.
2. While traditionally an initial elevation phase is
expected at stations located seaward of subduction
zones, a small initial depression phase was
observed at some DART stations.
3. Tsunami governing periods were 21.1 ± 1.7 min
and 14.7 ± 0.7 min, corresponding to a fault
length of 60–70 km and a fault width of
40–45 km.
4. According to the wavelet analysis, while the two
21-min and 15-min signals appeared in most
DART stations during *0.5 h following the con-
ventional arrival times, the 15-min signal was
delayed at some far-field stations.
5. Distribution of maximum DART wave heights
across the Pacific Ocean showed that a meaningful
relation between DART wave heights and direc-
tivity or distances from the source cannot be
established, at least for this tsunami.
Acknowledgments
The sea level data used in this study were provided
through the USA National Oceanographic and
Figure 7Wavelet analysis for the DART records during the 1 April 2014
tsunami from the Iquique (Chile) earthquake. The vertical black
and white lines represent the origin time of the earthquake and the
conventional tsunami arrival times, respectively. Time-averaged
wavelet spectrum over the time window is plotted to the right of
each wavelet plot. Vertical axes for the spectra are the same as the
wavelet plots. GWS stands for the global wavelet spectrum
b
Iquique Tsunami of April 2014 in the Pacific Ocean
Atmospheric Administration (NOAA). We thank
Hiroshi Tsuruoka and Takeo Ishibe at the Earthquake
Research Institute (ERI) for assisting in preparation
of some figures. Several figures were drafted using
the GMT software (WESSEL and SMITH 1991). We are
sincerely grateful to Prof. Alexander Rabinovich, the
editor, and two anonymous reviewers for comments
that improved this article. This study is supported by
the Japan Society for the Promotion of Science
(JSPS).
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